Change HMAC::Sign() to take base::StringPiece instead of string.

crypto/hmac.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Utility class for calculating the HMAC for a given message. We currently
 // only support SHA1 for the hash algorithm, but this can be extended easily.
 
 #ifndef CRYPTO_HMAC_H_
 #define CRYPTO_HMAC_H_
 #pragma once
 
 #include <string>
 
 #include "base/basictypes.h"
 #include "base/memory/scoped_ptr.h"
+#include "base/string_piece.h"
 
 namespace crypto {
 
 // Simplify the interface and reduce includes by abstracting out the internals.
 struct HMACPlatformData;
 
 class HMAC {
  public:
   // The set of supported hash functions. Extend as required.
   enum HashAlgorithm {
     SHA1,
     SHA256,
   };
 
   explicit HMAC(HashAlgorithm hash_alg);
   ~HMAC();
 
   // Returns the length of digest that this HMAC will create.
   size_t DigestLength() const;
 
   // TODO(abarth): Add a PreferredKeyLength() member function.
 
   // Initializes this instance using |key| of the length |key_length|. Call Init
   // only once. It returns false on the second or later calls.
   // TODO(abarth): key_length should be a size_t.
   bool Init(const unsigned char* key, int key_length);
 
   // Initializes this instance using |key|. Call Init only once. It returns
   // false on the second or later calls.
   bool Init(const std::string& key) {

[wtc, 2011/06/02 19:56:48]

Can you also change 'key' to a StringPiece, and remove
the <string> header inclusion on line 12 above?

     return Init(reinterpret_cast<const unsigned char*>(key.data()),
                 static_cast<int>(key.size()));
   }
 
   // Calculates the HMAC for the message in |data| using the algorithm supplied
   // to the constructor and the key supplied to the Init method. The HMAC is
   // returned in |digest|, which has |digest_length| bytes of storage available.
   // TODO(abarth): digest_length should be a size_t.
-  bool Sign(const std::string& data,
-            unsigned char* digest,
+  bool Sign(const base::StringPiece& data, unsigned char* digest,
             int digest_length) const;
 
   // TODO(albertb): Add a Verify method.
 
  private:
   HashAlgorithm hash_alg_;
   scoped_ptr<HMACPlatformData> plat_;
 
   DISALLOW_COPY_AND_ASSIGN(HMAC);
 };
 
 }  // namespace crypto
 
 #endif  // CRYPTO_HMAC_H_